1. Field of the Invention
The invention relates to optical fiber fabrication.
2. Discussion of the Related Art
Glass optical fiber has become a significant transmission medium in recent years, and its prevalence in communications systems is expected to increase. Glass optical fiber is generally produced from a glass preform, the preform typically consisting of a doped silica core surrounded by an inner silica cladding and a silica overcladding. As reflected in FIG. 1, and discussed in F. DiMarcello et al. "Fiber Drawing and Strength Properties," Optical Fiber Communications, Vol. 1, Academic Press, Inc., 1995, at 179-248, the preform 12 is generally arranged vertically in a draw tower 10 such that a portion of the preform 12 is lowered into a furnace region 14 that typically heats the preform 12 to temperatures around 2200.degree. C. The portion of the preform 12 placed into the furnace region 14 begins to melt, and the lower end of the preform 12 forms what is known as the neck-down region 16, which is where the preform glass flows from the original cross-sectional area of the preform 12 to the desired cross-sectional area of the fiber 18. From the lower tip of this neck-down region 16, the optical fiber 18 is drawn. As the preform glass is drawn into fiber 18, the preform 12 continues to be lowered into the furnace region 14, until the preform 12 is exhausted.
Clearly, the need to interrupt this fiber drawing process to put a new preform in place reduces efficiency of the process and reduces the consistency of the resultant fiber. Specifically, significant down-time is accumulated when putting new preforms in place and performing the initial drop of the preform into draw position. Moreover, significant waste is generated in re-establishing the draw from each new preform. Thus, techniques for fabricating more fiber from a single preform have been sought. However, the length of preforms is somewhat limited by the processes used to make them, and increasing preform diameter has therefore been considered to be the primary method for improving the efficiency of fiber fabrication. Yet, the parameters for consistently obtaining commercially acceptable fibers from such larger diameter preforms are not clear. Problems encountered with the current preforms are likely to be exacerbated in larger diameter preforms, and new, unforeseen problems are also likely to arise.
Thus, improved methods for more efficiently fabricating optical fiber are desired, in particular methods that reduce down-time and waste.